FAQ

What is a heat battery and how does it work?

A heat battery is a device that enables storage of heat energy when available in excess, so that it can be used at a later point in time, when needed. The HEAT-INSYDE heat battery makes use of a salt hydrate that can store and release heat with high energy power. It is a thermochemical storage technology: it uses water and salt, which undergo a reversible reaction with each other. As long as the water is not in contact with the salt, the heat is stored. This ensures that thermochemical storage is a very good storage solution if heat has to be stored for a longer period of time (more than 2 days).

Why is the heat battery needed?

Renewable energy sources are in continuous development and increasing use. However, a downside is that their energy production is weather dependent. Solar energy will not be produced in sufficient quantities on a grey day and not enough wind energy will result on a windless day. On the other hand, intensely sunny or windy days may produce excess solar or wind energy that will go unused. A heat battery is a device that enables storage of energy when produced in excess so that it can be used at another point in time, when needed. Energy produced in excess can be stored in many ways, for instance as electric energy in batteries, as mechanical energy by pumping water up into a reservoir, as direct heat energy by heating up a water tank or by conversion into fuels. All storage solutions come with very different characteristics in terms of speed, efficiency and, of course, cost. Depending on the application that the energy is needed for, a different storage technology might be preferable. For supplying a household with heating and warm water, a heat battery offers a very suitable and competitive storage solution.

What is the storage volume in the heat battery?

The volume of storage required to store a certain amount of energy is determined by the storage capacity. The HEAT-INSYDE battery works at a storage capacity of 600 MJ/m3. This means that for a typical 4-person household (energy demand of 50 MJ/day) and a storage period of 2 weeks the storage volume is comparable to that of a storage vessel of a small refrigerator.

How heavy is the device?

The actual storage material has an energy content of 0.5 MJ/kg. The total weight of the heat battery will thus depend on the amount of energy one wants to store. Assuming a storage period of up to 2 weeks and a typical 4-person household (energy demand of 50 MJ/day) then 600 MJ will need to be stored. The storage material will, therefore, roughly weigh 1200 kg. However, on top of this another 600 kg need to be added to account for the other heat battery components, such as the exchanger, pumps, etc.

At which temperature does the battery release its heat?

The battery uses a chemical reaction with water vapor. The temperature at which the heat can be released depends on the temperature of the water that is available. The battery will be able to bring a temperature increase of 40-50 °C. So the battery can deliver heat at 50 °C if the source is 10 °C, but also 100 °C if the cold source is 60 °C. Tap water supply (typically at 65 °C) and heating (typically in a range of 30-45°C) are therefore excellent application cases for the heat battery.

What temperature is required to charge the battery?

The volume of storage is determined by the storage capacity. The HEAT-INSYDE battery works at a storage capacity of 600 MJ/m3. This means that for a storage period of 2 weeks the storage volume is comparable to that of a storage vessel of a small refrigerator.

When will the battery become available to the consumer?

At the moment, the heat battery is not commercially available. We are working hard to have a user-ready-prototype available soon. This will take at least another 2 years. The user-ready prototype will need to be tested by end-users and depending on the results, the product will be available for the consumer.

Are you still looking for DEMO locations?

In the next couple of years, the battery will be further tested in the lab, but also with end-users in the Netherlands, Poland and France. Initially, testing will be conducted with a small group of end-users. We will expand this test group, but most probably not within the H2020 project HEAT-INSYDE.

Is my house suitable for the HEAT-INSYDE battery?

As with most renewable energy innovations, it is desirable for your house to be sufficiently insulated that low temperature heating can be used. If this is the case, the battery will function properly in combination with other renewable sources and the necessary storage space is in the order of a small refrigerator. The size will depend strongly on the type of home (detached, terraced house, apartment) and on the type of residents (single, family, seniors). Within the Horizon 2020 project HEAT-INSYDE we will determine the improved performance of the energy systems with the heat battery.

What are the main differences compared to a water buffer?

The most important difference is the storage period, which is infinite for our heat battery. A water buffer will always lose energy to its environment during storage because it uses the heat capacity of water. This is not the case with the thermochemical storage technology in the HEAT-INSYDE battery: it uses water and salt, which undergo a reversible reaction with each other. As long as the water is not in contact with the salt, the heat is stored. This ensures that thermochemical storage is a much better system if heat has to be stored for a longer period of time (more than 2 days).